Dear Simulia,

I am doing research for modelling nonlinear soil reactions for jacket founded offshore wind turbine. It is in combination with using Substructures for the foundation model (soil+piles) called a Seismic Superelement (SSE).

I have trouble getting the same steady state response from both the Complete model (FE Z100 model) and the model that includes a Substructure (SSE model Z103, with Substructure Z103).

I am using a simplified model, it includes two parts:

1 Substructure

-beam

-springs (soil) in two directions 

2 Another structure

-beam

The two parts are coupled using a kinematic coupling.

Substructure Z103: For generating the substructure I am using a frequency step to not only get the Guyan modes, but also vibrational modes. I am using a direct steady-state to see if the two models are the same.

The end parts of the springs are supposed to be available for displacement loading (for simulating earth motions).

Right now I have restrained the retained DOFs to zero displacement for the Direct Steady-State plot and for the Frequency Analysis. I am uncertain about the setup of the Boundary Conditions in the Substructure to carry over the proper information (vibrational modes etc.). However, I expected the frequency response to be the same with the current setup.

I have added the results for the Direct Steady-state for the Top Node of Part 2 in Excel. It can be seen that they are not equal.

Can you please help me understand why there is a difference and how/if I can make them equal again?

Kind regards,

Martin Dirkzwager

Abaqus ​​​​​​​